Seals are used to minimize leakage of fluids. A known seal is a cloth seal having a generally impervious shim assemblage and a cloth assemblage generally surrounding the shim assemblage. Cloth seals may be used in many applications including, but not limited to, seal assemblies for steam turbines and gas turbines used for power generation and seal assemblies for gas turbines used for aircraft and marine propulsion.
A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine area of a gas turbine will lower the efficiency of the gas turbine leading to increased fuel costs. Also, gas-path leakage in the combustor area of a gas turbine will require an increase in burn temperature to maintain power level, such increased burn temperature leading to increased pollution, such as increased NOx and CO production.
Gas-path leakage occurs through gaps between larger gas turbine components such as through gaps between the combustor and the turbine, and gas-path leakage occurs through gaps between smaller gas turbine components such as through gaps between combustor casing segments. Such components have surfaces of different shapes, suffer from assembly misalignment, and undergo vibration. For example, vibration is particularly important during startup of a turbine rotor which must pass through one or more critical frequencies before reaching operational speed. Also, hot section components, such as combustors and turbines, thermally experience hot gas flow and typically undergo different thermal growths. Steampath leakage occurs through gaps between steam turbine components in a manner similar to that for gas-path leakage through gaps between gas turbine components.
Cloth seal installations have been proposed for use in gas-path leakage gaps of gas turbines and for use in steam-path leakage gaps of steam turbines. However, such conventional cloth seal assemblies cannot handle large changes in the size of the leakage-path gap between the two components and therefore have not been proposed for use in such "large gap change" applications. A conventional cloth seal assembly used in such a "large gap change" application would have the cloth seal become crimped (i.e., nonelastically bent) when the gap between the two components became very small and thereafter would not seal when the gap returned to normal or became very large.
Conventional seals used in such "large gap change" applications include a conventional rigid or leaf seal made of metal which may have a leakage of 2.4% (primarily from flow around the seal due to different surface shapes, assembly misalignment, vibration, thermal growth, and/or wear). Such leakage in the combustor may result in a 15 (or much higher) parts-per-million (ppm) NOx production and a similar CO production. It is noted that conventional rigid or leaf seals do not seal as well as cloth seals. What is needed is an improved seal assembly having a flexible cloth seal that can accommodate large changes in the size of the gas-path leakage gap due to vibration, thermal differential expansion, etc.